Cobalt containing compounds have heretofore been compounded with vulcanizable rubber skim stocks to promote adhesion of the latter to metal. A typical method for improving adhesion is set forth in U.S. Pat. No. 3,897,583 which is directed toward the adhesion of metal to rubber by incorporating a cobalt salt in a rubber stock which contains an adhesive resin forming system based on a methylene donor which is a methylolated nitroalkane in combination with a resorcinol type methylene acceptor. Cobalt salts disclosed include those of aliphatic or alicyclic carboxylic acids having 6-30 carbon atoms.
Similarly, U.S. Pat. No. 3,903,026 discloses a rubber composition containing cobalt carboxylate and magnesium oxide to improve the adhesion between the rubber and zinc or zinc alloy plated steel.
And, U.S. Pat. No. 3,936,536 discloses the method of adhering rubber to metal by coating the metal with rubber containing a small amount of Co(NH.sub.3).sub.2.Cl.sub.2.
Turning from the art of metal adhesion to that of metallic salts, U.S. Pat. No. 4,060,535 discloses a process for producing metal salts of organic acids by vigorously agitating a mixture of appropriate amounts of the metal oxide, hydroxide or carbonate and the organic acid in water. Among the metals recited is cobalt and among the organic acids is .rho.-aminobenzoic acid. From the examples provided by the patentee, however, it is clear that a true salt was formed and not a chelate structure. Moreover, the metal salt contains up to about 8% by weight of water and up to 1% by weight of free acid. The patent contains no reference to the use of the metal salt as an adhesion promoter and, in fact, would not be useful as such inasmuch as presence of any acid would be likely to lengthen the cure time of the rubber skim stock and could also effect weaker tensile strengths of the product.
Thus, none of these patents discloses a method for the preparation of anhydrous cobalt chelates much less suggests that the chelate could be added to vulcanizable rubber skim stocks as an adhesion promoter.